refactor flight app support code into src/apwrapper lib
flight sensors task uses new sensors capture interface
flight app had depleted 64k freertos heap, bumped up to 96k

* remember, uart queues use 3k to queue 1k of data...
flight main.cpp: launch main task as high priority, then delete

along with making sure xTaskCreate wrapper hangs on failure,
this ensures system doesn't run unless all tasks are created
successfully.
bump mavlink submodule: lee's debug messages in mavproxy are less chatty